1. Field of the Invention
The present invention pertains to improvements in breakaway mechanisms designed to protect a pipeline tie-in to an offshore platform, or an existing pipeline, or a subsea structure such as a wellhead, by installing a weak link commonly known as a breakaway device, in a new pipeline.
2. Description of Prior Art
Breakaway protection for offshore structures is primarily required against soil movements or mud slides which can subject a pipeline to extremely large tension loads. Breakaway protection is also often used against seismic loads and against anchor hooking loads for tie-ins which may be severely damaged by such loads, especially in areas where there are frequent seismic events and in other areas where there is considerable floating construction activity or floating drilling activity nearby. In addition to breakaway protection, there is often a need for a certain elastic flexibility in a pipeline system which can absorb small movements of the pipeline due to thermal expansion or trawl gear impacts, without damaging or shutting down the pipeline.
The art provides various commercial safety joints and pipeline couplings, which are designed to pull apart at a specified load, independently of the pipeline pressure, temperature, or applied bending moments. These devices depend upon mechanical pistons, seals, and breaking mechanisms for operation, and are often installed in tandem with a check valve to minimize loss of internal fluid in the event of a break. The breakaway load for a commercial safety joint normally is chosen to be sufficiently high to prevent inadvertent breaking, but yet low enough to be safely below that which would damage the platform, pipeline, or a subsea structure. Thus, for a J-tube riser on to a fixed platform, the breakaway load normally is set between 400 and 800 kips, since the platform structure can safely withstand such loads, whereas, for a tie-in to an existing pipeline or a subsea wellhead, the selected breakaway load would have to be considerably less.
Experience with these joints has occasionally resulted in inadvertent safety joint failures, at tension loads well below their design loads, and has called into question the reliability of the commercial safety joint. Each failure required an expensive repair involving costly offshore equipment and divers. While there is no evidence to indicate that a mechanical safety joint will not function as designed once properly installed, the overall cost of such devices may become prohibitive if the incidence of premature failures were to become more frequent.
Accordingly, the present invention is directed to overcoming the above-noted problems in the art and to providing a solution as more particularly described hereinafter.